What kind of ducks do you have or will be getting? Mid and larger sized ducks are well insulated and do well in the cold. A ventilated coop will keep them out of the wind when needed but still allow it not to get stuffy. They need ventilation. I built my coop with openings at the top of the walls covered with 1/2" hardware cloth (well secured) in the ends with the roof overhangs structured such that rain and snow won't blow in but will allow air to circulate. No insulation and they do very well in the winter. I use the deep litter bedding method which helps keep the floor warm. There were only a few nights when it got down to zero that it crusted over some but most days I was able to stir it up after it got about 5 inches deep.

I have one vent on the sidewall away from the prevailing wind and one in the door that I can open and close depending on the weather and temperature but generally leave them open in the summer no matter the weather as ducks really need ventilation when it is hot. My ducks are in the coop only at night also. The coldest winter days don't seem to bother them even during high winds and they prefer to be on the pond than in the coop during daylight (I am fortunate enough to have a spring fed pond that doesn't freeze in the winter and this makes it easier to manage ducks in the winter. I don't know whether or not they would use the coop more if not for the pond).

I have Khaki Campbells that are quite winter hardy. Some smaller breeds are not as cold hardy.

Thank you!
We have khaki campbells and we're planning to convert an old horse stall into the coup - it'll have an opening for them to get into the attached covered run we're going to enclose, and I'll need to decide how many windows we should add if any and what to do about the door. Right now it has a split door on the side where it's not as windy - we could easily make the top half of that door screened with hardware cloth for ventilation. Would that be enough or would it need more than that?

How large is the door? I built my coop with a split door (upper and lower) and have hardware cloth in the upper door that I can also cover up during cold weather. I have a vent above the door (door is on front of coop) and one in the rear wall (about 2 feet wide and 8 inches high) so there is flow through which I think is important. Do you have photos you could send?